This invention relates to the use and application of radiant energy within the human body for the controlled removal or etching away, for example, by ablation, of tissue or other biological material, in particular the removal of a vascular obstruction. The treatment of vascular obstructions including peripheral as well as coronary vascular obstructions, has been the subject of much investigation in recent years. Vascular surgery in which a diseased vessel is removed and replaced with a graft, or in which the blocked region of the vessel is bypassed with a graft, has become relatively common. Nevertheless, it is desirable that procedures and techniques be improved to reduce the level of trauma to a patient so as to simplify the procedure and treatment for the patient but without sacrificing effectiveness. While procedures for surgical removal and by-passing of vascular obstructions have become well developed, it clearly is desirable to provide alternatives to such non-conventional surgical procedures.
Among the alternatives which have been developed is the angioplasty procedure in which devices such as the balloon dilatation catheter of the type illustrated in Gruntzig U.S. Pat. No. 4,195,637, are used to open a passage through a vascular obstruction. In the balloon dilatation technique a catheter having a special balloon at its distal end is advanced through the patient's blood vessels until the balloon is placed within the obstruction. The balloon then is expanded under substantial pressure to forcibly enlarge the lumen within the blood vessel. When the procedure is successful the lumen of the blood vessel remains open after the balloon has been deflated and removed. The material which caused the obstruction, typically arterial plaque, is compressed radially outwardly. Those patients who can be treated successfully with the dilatation technique are spared the trauma, time and expense of traditional vascular surgery. However, the angioplasty technique cannot be used to treat all vascular obstructions and, indeed, the majority of obstructions cannot be treated in that manner.
When an obstructed vessel is treated surgically by replacement or bypass of the vessel, the diseased portion of the vessel either is removed in its entirety or is permitted to remain, in its obstructed condition, in the patient but with a bypass vessel grafted across the blocked regions. In the angioplasty technique the plaque which formed the obstruction remains in the artery although in a compressed condition. In some instances the plaque and vessel wall may rearrange themselves after some time to begin to obstruct the vessel again.
Although the general desirability of recanalizing an obstructed blood vessel by removal of the vascular obstructions from the vessel has long been recognized, no effective system or treatment technique has yet been discovered or developed for that purpose. The possibility of using laser energy for that purpose also has been recognized for some time. While recent availability of laser sources of controllable radiant energy have been found useful for some surgical operations, such as in certain kinds of eye surgery, no suitable device and technique have been developed by which a beam of radiant energy such as laser energy can be applied to a vascular obstruction to selectively and controllably remove that obstruction without causing trauma to the vessel, so as to leave the natural vessel in a healthy, unblocked, recanalized and functioning condition.
Proposals and efforts to apply laser energy to remove a vascular obstruction have encountered numerous difficulties. Prior efforts to deliver a beam of laser energy typically have involved the use of various configurations of catheters having arrangements of fiber optical conductors to conduct the radiant energy into the patient's vessel in an effort to direct the beam to the obstruction so as to destroy the obstruction. No devices or techniques have been developed by which it was possible to control effectively the beam. If the beam is not aligned properly in the blood vessel it can impinge against the lining of the blood vessel thereby damaging the vessel wall and possibly puncture the wall. Even if the beam is aligned properly in the blood vessel, the lining of the vessel can be damaged or the vessel can be punctured if there is a bend in the vessel just distal of the location of the obstruction.
Also among the significant difficulties encountered in trying to use laser energy to clear vascular obstructions is the tendency of the laser beam to cause biological material to char in the region surrounding the target. Such charring results, at least in part, from poor control over the manner and amount of energy applied. In the context of a delicate blood vessel, charring can present very serious problems, possibly doing severe damage to the surrounding tissue. Additionally, any biological material which becomes charred and adheres to the distal tip of the optical fiber conductor prevents emission of the beam from the distal tip of the conductor. In that case, the material at the end of the conductor becomes highly heated which, in turn, causes overheating and destruction of the optical fiber.
Other difficulties relate to the manner of positioning and locating the distal end of the catheter so that it is positioned properly with respect to the obstruction. Prior proposals which have included the use of supplemental optical fibers to transmit illuminating light into the blood vessel in conjunction with other groups of fibers to permit visual observation of the interior of the blood vessel are not practical because they are too large and too stiff for use in coronary arteries. Another difficulty is that there often may be material such as blood in the region between the emission point of the laser beam at the end of the fiber and the obstruction. Such material may obstruct the optical path. The blood may become charred at the distal emitting tip of the fiber which, as described above, can result in overheating and destruction of the optical fiber.
All of the foregoing difficulties have been complicated by the dimensional limitations imposed on any catheter which is to be inserted into a blood vessel, particularly narrow blood vessels such as coronary arteries which can have lumens of the order of 1.5 to 4.5 millimeters diameter.
The present invention relates to new catheter systems for delivering radiant energy to a selected site within a blood vessel in a manner which enables the radiant energy to be applied controllably to an obstruction and in a manner which avoids the foregoing and other difficulties.